Prepreg Types and Selection Techniques in PCB Manufacturing

Prepreg Types: Prepreg (PP) is a key dielectric material used in PCB (Printed Circuit Board) lamination, serving as an insulating and bonding layer between copper foils and core substrates. Choosing the right prepreg type is critical for achieving reliable electrical performance, mechanical strength, and thermal stability in multilayer PCBs. Prepreg comes in different glass fabric styles such as 7628, 2116, 1080, and 106, each with specific resin content, thickness, and flow characteristics that influence PCB performance.

This article explores the different types of prepreg fabric styles, their properties, and essential selection techniques to ensure optimal PCB performance.

Common Prepreg Types Used in PCB Manufacturing process

Prepreg is classified based on glass weave type, which impacts mechanical strength, resin retention, and dielectric performance. Below are the most commonly used prepreg types:

1. 7628 Prepreg (Thick and High Resin Content)

Thickness: ~7 mils (0.18 mm)

Glass Weave Density: Coarse

Resin Content: High (~50%)

Key Properties:

Provides high mechanical strength.

Best suited for thicker PCB stack-ups.

Higher resin content helps with void filling and adhesion.

Application: Used in power PCBs, automotive boards, and thick multilayer constructions.

2. 2116 Prepreg (Medium Thickness)

Thickness: ~4.3 mils (0.11 mm)

Glass Weave Density: Medium

Resin Content: Medium (~45%)

Key Properties:

Provides a balance between thickness and flexibility.

Moderate resin flow for consistent bonding.

Suitable for general-purpose multilayer PCBs.

Application: Used in telecommunications, industrial electronics, and general multilayer PCB designs.

3. 1080 Prepreg (Thin and Low Resin Content)

Thickness: ~2.3 mils (0.058 mm)

Glass Weave Density: Fine

Resin Content: Low (~40%)

Key Properties:

Thin profile allows for high-density interconnects (HDI).

Reduces dielectric loss for better signal integrity.

Used where low thickness is critical.

Application: Ideal for high-speed PCBs, HDI designs, and RF/microwave applications.

4. 106 Prepreg (Ultra-Thin and Low Flow)

Thickness: ~1.4 mils (0.036 mm)

Glass Weave Density: Ultra-fine

Resin Content: Very low (~38%)

Key Properties:

Best suited for ultra-thin PCB laminations.

Provides excellent electrical performance in high-frequency applications.

Minimal resin flow ensures precise thickness control.

Application: Used in flexible PCBs, high-speed digital circuits, and RF designs.

Key Factors for Selecting Prepreg types in PCB Lamination

Choosing the right prepreg depends on several factors, including design requirements, electrical performance, and manufacturing constraints. Below are the critical selection techniques:

1. Determine the Required Resin Content (RC%)

Higher RC%:

Suitable for high-resin flow applications.

Helps in void filling and reducing delamination risks.

Lower RC%:

Used where minimal flow is needed.

Preferred for rigid stack-ups with controlled thickness.

2. Consider the Glass Transition Temperature (Tg)

For standard PCBs: FR-4 prepreg with Tg 130°C–150°C is sufficient.

For high-temperature applications: Use high-Tg prepregs with Tg 170°C–250°C+.

3. Evaluate Dielectric Performance (Dk & Df)

For high-speed PCBs:

Select low-Dk prepregs to reduce signal distortion.

Lower Df improves signal integrity in high-frequency circuits.

4. Assess Prepreg Thickness and Number of Layers

Thick Prepreg (7628, 2116):

Used in power boards and structural reinforcement.

Thin Prepreg (1080, 106):

Preferred for fine-pitch and high-density interconnect (HDI) PCBs.

5. Compatibility with Copper Foil and Core Material

Ensure prepreg matches the core material’s CTE and expansion properties to prevent layer separation.

Use similar resin systems to achieve better adhesion and reliability.

6. Moisture Absorption and Storage Conditions

Store prepreg in low-humidity, controlled environments.

Use before expiration to maintain consistent resin flow and bonding properties.

Quality Control Measures for Prepreg Types Selection

To ensure the best performance and reliability, manufacturers implement strict quality control checks:

1. Prepreg Thickness Verification

Measures actual thickness vs. design specifications using precision micrometers.

2. Resin Flow Testing

Evaluates how well the prepreg resin flows during lamination.

3. Dielectric Property Testing

Verifies Dk and Df values to maintain signal integrity in high-speed PCBs.

4. Thermal Stability and Peel Strength Tests

Ensures laminated layers remain intact under extreme conditions.

5. Moisture Absorption Analysis

Checks prepreg’s resistance to humidity, which affects electrical performance.

Conclusion

Selecting the appropriate prepreg materials for PCB lamination is critical to ensuring reliable electrical performance, mechanical strength, and overall manufacturing efficiency. By understanding the different prepreg fabric types, resin characteristics, and selection methods, manufacturers can significantly enhance PCB fabrication and improve long-term reliability.

As technology advances with high-speed PCB, high-frequency PCB, and HDI PCB designs, opting for prepregs with low-Dk, high-Tg properties, and suitable glass weave can optimize performance in modern electronics. SQPCB stands out as a trusted provider of high-quality prepreg materials, ensuring optimal lamination that supports the stringent demands of today’s cutting-edge electronic devices.

With SQPCB’s advanced materials and expertise, you can streamline your PCB production while maximizing product performance, making it the ideal partner for achieving superior quality and reliability in every PCB.

Frequently Asked Questions (FAQ)

What are the key factors to consider when selecting prepreg for PCB lamination?
When selecting prepreg, consider factors like resin type, glass weave, dielectric constant (Dk), and the glass transition temperature (Tg). These properties will affect the electrical performance, mechanical durability, and heat resistance of the PCB.

How do low-Dk prepregs enhance PCB performance?
Low-Dk prepregs help reduce signal loss and crosstalk in high-speed, high-frequency PCBs, making them ideal for applications in communications, RF circuits, and high-performance computing systems.

What is the difference between high-Tg and low-Tg prepregs?
High-Tg prepregs are more heat-resistant and are suitable for applications exposed to higher temperatures, while low-Tg prepregs are typically used in standard applications where the temperature range is not as demanding.

How does glass weave impact the performance of prepreg?
The type of glass weave influences the mechanical strength, rigidity, and dimensional stability of the PCB. A finer glass weave provides better performance in high-density designs, while a coarser weave can offer increased durability in rugged environments.

Why should I choose SQPCB for PCB lamination?
SQPCB provides premium prepreg materials and expertise in PCB lamination. Their advanced manufacturing processes ensure optimal material selection and high-quality production, making them a reliable partner for your PCB needs.